Heat dissipation device for led chips

ABSTRACT

A heat dissipation device for removing heat from LED chips includes a finned heat sink, a plurality of heat pipes and a plurality of heat conductive substrates. The heat sink comprises a base plate and a plurality of fins formed on the base plate. The heat pipes which transfer heat in a unidirectional manner are embedded in the base plate. Each of the heat pipes defines a first wall and a second wall coupled to the heat sink. The heat pipes only transfer heat from the first walls to the second walls and restrict a heat transfer in a reversed direction. The substrates are in contact with first walls of the heat pipes. The LED chips are mounted on the substrates. When the LED chips generate heat, the heat is transferred to the fins via the unidirectional heat pipes to lower the temperature of the LED chips.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat dissipation device and particularly to a heat dissipation device for removing heat from LED chips.

2. Description of Related Art

An LED lamp is a type of solid state lighting that utilizes light-emitting diodes (LEDs) as a source of illumination. An LED is a device for transferring electricity to light by using a theory that, if a current is made to flow in a forward direction in a junction comprising two different semiconductors, electrons and holes are coupled at the junction region to generate a light beam. The LED has an advantage in that it is resistant to shock, and has an almost eternal lifetime under a specific condition; thus, the LED lamp is intended to be a cost-effective yet high quality replacement for incandescent and fluorescent lamps.

A high-powered LED light device produces considerable amount of heat, which may cause performance degrade or even damage of the device if the heat is not removed from LED chips of the device efficiently. In an LED light device, the LED chips which are mounted on a substrate are the core for generating light and heat. A transparent cover may be used to cover the LED chips for protecting the LED chips from foreign articles. Although there are many different designs, the major heat dissipation route for the heat produced by the LED chips is usually managed through the substrate to which the LED chips are mounted and a metal heat sink thermally connecting with the substrate.

When the LED light device is used as an outdoor LED lamp, it usually requires a waterproof sealing for the LED chips to protect the LED chips from rain. The LED lamp comprises a heat sink for dissipating heat generated by the LED chips. In a sunny day, the heat sink is exposed directly to the sunlight and heated by sunlight. The heat absorbed by the heat sink from the sunlight is transferred to the LED chips which are in contact with the heat sink. Therefore, the temperature of the LED chips raises enormously, which affects the life-span of the LED chips.

What is needed, therefore, is a heat dissipation device for an LED light device which has an improved structure and overcomes the abovementioned disadvantage.

SUMMARY OF THE INVENTION

A heat dissipation device for removing heat from LED chips includes a finned heat sink, a plurality of heat pipes and a plurality of heat conductive substrates. The heat sink comprises a base plate which defines a first surface and a second surface opposite to the first surface. A plurality of fins are formed on the second surface of the base plate. The heat pipes of unidirectional heat transfer are embedded in the first surface of the heat sink. Each of the heat pipes defines a first wall and a second wall coupled to the heat sink. The heat pipes only transfer heat from the first walls to the second walls and restrict a heat transfer in a reversed direction. The substrates are in contact with first walls of the heat pipes. The LED chips are mounted on the substrates. When the LED chips generate heat, the heat is transferred to the fins of the heat sink via the substrates and the unidirectional heat pipes to lower the temperature of the LED chips.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiment. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric, assembled view of a heat dissipation device in accordance with a preferred embodiment of the present invention;

FIG. 2 is an explored view of the heat dissipation device of FIG. 1; and

FIG. 3 is a view similar to FIG. 2, but from an opposite direction.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, a heat dissipation device is used for removing heat from LED chips 100 housed in an outdoor LED lamp (not shown). The heat dissipation device comprises a heat sink 10, a plurality of heat pipes 20 embedded in the heat sink 10 and multiple substrates 30 in contact with both the heat pipes 20 and the heat sink 10. The LED chips 100 are mounted on the substrates 30 and arranged in matrixes.

The heat sink 10 is integrally formed by aluminum extrusion. The heat sink 10 comprises a rectangular base plate 12 and a plurality of fins 14 formed on the base plate 12. The base plate 12 defines a first surface 122 facing the substrates 30 and a second surface 124 opposite to the first surface 122. A plurality of receiving grooves 120 complementary to the heat pipes 20 is defined in the first surface 122. The receiving grooves 120 can be various shapes such as L-shaped, U-shaped and S-shaped etc., in accordance with the configurations of the heat pipes 20. In this embodiment, the receiving grooves 120 and the heat pipes 20 are straight in shape. The receiving grooves 120 are divided into two groups each comprising three elongated, straight grooves 120 juxtaposed closely to each other. The grooves 120 are parallel to two opposite lateral sides of the base plate 12. The fins 14 extend from the second surface 124 of the base plate 12 and can be constructed in various configurations to maximize heat-exchanging area of the heat sink 10.

The heat pipes 20 are divided into two groups, each comprising three heat pipes 20. Each of the heat pipes 20 is elongated, straight and flat and comprises a casing (not labeled). The casing defines a first wall 22 facing the substrates 30 and a second wall 24 parallel to the first wall 22 and facing the heat sink 10. Each of the heat pipes 20 is designed to be a unidirectional heat transfer device, which means that the heat pipe 20 can only transfer heat in a direction from the first wall 22 to the second wall 24 and inhibits the heat transfer in a reversed direction, when the first wall 22 faces downwardly. Each of the heat pipes 20 is provided with a capillary wick (not shown) in the casing thereof for achieving the unidirectional heat transfer. The capillary wick may be a plurality of fine grooves defined in a lengthwise direction of the casing, a fine-mesh wick, or a layer of sintered metal/ceramic powders only formed on an inner side of the first wall 22 distant from the second wall 24. The casing is half filled with working liquid (not shown) which acts as a heat carrier for carrying thermal energy from the first wall 22 to the second wall 24 and the working liquid is just enough to submerge the capillary wick adjacent to the first wall 22 when the first wall 22 faces downwardly toward the ground. The first surface 122 of the heat sink 10 is coplanar with outer surfaces of the first walls 22 when the heat pipes 20 are received in the grooves 120 of the heat sink 10.

The substrates 30 each are formed from a material having a high heat conductivity, such as copper. Each of the substrates 30 is a flat plate and defines a first surface 32 and a second surface 34 opposite to the first surface 32 and facing the heat sink 10. The LED chips 100 are mounted on the first surfaces 32. The second surfaces 34 are kept in contact with and coupled with the first surface 122 of the heat sink 10 and the outer surfaces of the first walls 22 of the heat pipes 20 by means soldering or adhering. Two substrates 30 are positioned on each group of the heat pipes 20.

In use of the heat dissipation device, the heat pipes 20 are received in the corresponding grooves 120 in the first surface 122 of the heat sink 10. The outer surfaces of the first walls 22 of the heat pipes 20 and the first surface of the heat sink 10 cooperatively form a contacting surface in contact with the second surfaces 34 of the substrates 30, wherein a major part of the second surfaces 34 of the substrates 30 are in contact with the heat pipes 20.

It is well known that the outdoor LED lamp is positioned in such a way that the first surface 122 of the base plate 12 of the heat sink 10 faces downward to the ground. In this way, the capillary wick near the first walls 22 of the heat pipes 20 is submerged in the working liquid while the second walls 24 of the heat pipes 20 are away from the working liquid; thus, heat accumulated in the heat sink 10 by absorbing heat from sunlight can not be transferred to the first walls 22 of the heat pipes 20 via the second walls 24, whereby the LED chips 100 are protected from being heated by heat of the heat sink 10. In other words, thermal resistance of the heat pipes 20 regarding the heat transfer from the heat sink 10 to the heat pipes 20 is greatly higher than that regarding the heat transfer from the heat pipes 20 to the heat sink 10. Accordingly, in daytime, when the outdoor LED lamp is not activated to generate light and is exposed to sunlight, heat of the sunlight will not heat the LED chips 100 via the heat sink 10. Meanwhile, in night, when the outdoor LED lamp is activated to generate light, the heat generated by the LED chips 100 can be effectively dissipated to air by the heat sink 10, where the working liquid in the heat pipes 20 has a continuous, two-phase circulation in the heat pipes 20 to transfer the heat of the LED chips 100 to the heat sink 10.

It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention. 

1. A heat dissipation device adapted for removing heat from LED chips, comprising: a heat sink comprising a base plate which defines a first surface and a second surface opposite to the first surface, and a plurality of fins formed on the second surface of the base plate; a plurality of heat pipes of unidirectional heat transfer being embedded in the first surface of the heat sink, each of the heat pipes defining a first wall and a second wall coupled to the heat sink, the heat pipes only transferring heat from the first walls to the second walls and restrict a heat transfer in a reversed direction; and a plurality of substrates in contact with first walls of the heat pipes, and the LED chips being mounted on the substrates; wherein when the LED chips generate heat, the heat is transferred to the fins via the unidirectional heat pipes to lower a temperature of the LED chips.
 2. The heat dissipation device as claimed in claim 1, wherein each of the heat pipes is provided with a capillary wick which has one of the following structures: a plurality of fine grooves defined in a lengthwise direction of the casing, a fine-mesh wick, or a layer of sintered metal/ceramic powders only formed on an inner side of the first wall and away from the second wall.
 3. The heat dissipation device as claimed in claim 2, wherein the heat pipes each are half filled with working liquid which is just enough to submerge the capillary wick adjacent to the first wall when the first wall faces downwardly toward the ground.
 4. The heat dissipation device as claimed in claim 1, wherein each of the substrates is a flat plate and defines a first surface on which the LED chips are mounted and a second surface opposite to the first surface.
 5. The heat dissipation device as claimed in claim 4, wherein the second surfaces of the substrates are coupled to the first surface of the heat sink and the first walls of the heat pipes.
 6. The heat dissipation device as claimed in claim 1, wherein the heat pipes each can be one of various shapes: straight, L-shaped, U-shaped and S-shaped, and the first surface of the heat sink defines corresponding receiving grooves accommodating the heat pipes therein.
 7. The heat dissipation device as claimed in claim 6, wherein the heat pipes each are straight and are juxtaposed closely to each other and respectively received in the corresponding straight receiving grooves.
 8. The heat dissipation device as claimed in claim 1, wherein the fins extend from the second surface of the base plate and can be constructed in various configurations to maximize a heat-exchanging area of the heat sink.
 9. A heat dissipation device adapted for removing heat from LED chips, comprising: a finned heat sink comprising a base plate; a plurality of heat pipes embedded in the base plate, each heat pipe comprising a casing which is half filled with working liquid and has a first wall and a second wall in contact with the base plate of the heat sink; and a plurality of heat conductive substrates each defining a first surface on which the LED chips are mounted and a second surface in contact with the heat pipes; wherein each of the heat pipes is provided with a capillary wick which has one of following structures: a plurality of fine grooves defined in a lengthwise direction of the casing, a fine-mesh wick, or a layer of sintered metal/ceramic powders only formed on an inner side of the first wall and away from the second wall, and working liquid which is just enough to submerge the capillary wick adjacent to the first wall when the first wall faces downwardly toward the ground.
 10. The heat dissipation device as claimed in claim 9, wherein the substrates each are a flat plate, the second surfaces of the substrates are coupled to the base plate of the heat sink and the first walls of the heat pipes, a major part of the second surfaces of the substrates being in contact with the first walls of the heat pipes.
 11. The heat dissipation device as claimed in claim 10, wherein the heat pipes each can be one of various shapes: straight, L-shaped, U-shaped and S-shaped, and the first surface of the heat sink defines corresponding receiving grooves accommodating the heat pipes therein.
 12. The heat dissipation as claimed in claim 10, wherein the heat pipes are straight and divided into two groups, and each group of the heat pipes are connected with at least two substrates.
 13. The heat dissipation device as claimed in claim 12, wherein the heat pipes of each group are juxtaposed closely to each other and respectively received in the corresponding straight receiving grooves.
 14. The heat dissipation as claimed in claim 9, wherein the base plate defines a first surface coupled with the second surfaces of the substrates and a second surface opposite to the first surface, and a plurality of fins are formed on the second surface of the base plate.
 15. An LED assembly comprising: a heat sink having a plurality of fins thereon; a plurality of heat pipes embedded in the heat sink; a plurality of heat conductive substrates coupled to the heat pipes; and a plurality of LED chips mounted on the substrates; wherein the heat pipes allow heat generated by the LED chips to be transferred to the heat sink via the substrates and the heat pipes, and inhibit heat in the heat sink to be transferred to the substrates via the heat pipes. 